Recently the Department of Transportation has focused on the problem of transporting hazardous materials in railway tank cars. In the event of a derailment and/or in the event of a bypassed coupler, it is possible for the tank to burst and the hazardous material escape and harm persons or property in the area.
Specifically, in the event of a bypassed coupler the coupler of one car can move up and puncture the tank of the adjacent car, causing the hazardous material to escape.
In order to alleviate this problem, the Department of Transportation has established that all tank cars carrying hazardous materials (112A340W, 112A400W and 114A500W in the 112 and 114 classification) must be provided with head shields.
The tanks for railway tank cars are in the heat treated condition. A head shield cannot simply be welded onto a heat treated tank car. The welding operation results in a heat affected zone which may be brittle and thus has a greater chance of bursting under pressure and/or in transit, and further such a welded unannealed tank car does not meet the requirements of the ASME Pressure Vessel Code.
A lug is readily applied to a new tank car prior to heat treatment which can be of sufficient outward extent that the weld heat affected zone will not extend to the tank when the head shield is subsequently welded in place to the lug.
However, a problem exists as to how to apply head shields to new cars not having such welding lugs and how to retrofit tank cars now in the service of hazardous materials with head shields, none of which have such head shield welding lugs.